JNITED STATES DEPARTMENT OF AGRICULTURE 

„ BULLETIN No. 924 4 

ififc % 

jjg? Contribution from the Bureau of Plant Industry > 

Jf&f^&J-U WM. A. TAYLOR, Chief f&F^mTU 





Washington, D. C. 



PROFESSIONAL PAPER 



January 26, 1921 



TEAR-STAIN OF CITRUS FRUITS. 

By John Kt Winston. 
Pathologist, Office of Fruit-Disease Investigations. 



CONTENTS. 



Page. 

Descripf ion of the disease 1 

Review oftbe literature 2 

Spraying experiments 3 

Cultural work 5 

Histological examinat ion 9 



Page. 

Inoculation experiments 9 

Conclusions 11 

Summary II 

Literature cited : 12 



DESCRIPTION OF THE DISEASE. 

Florida citrus fruits are subject to two distinct types of tear 
streaking, namely, wither-tip tear-stain and melanose tear-streak. 
The former has been attributed to Colletotricfium gloeosporioides 
Penz., while the latter, which will not be discussed in this bulletin, 
is doubtless due to a peculiar distribution of the spores of the 
causal organism (Phomopsis citri Fawcett) in trickling waters. 

Wither-tip tear-stain is a smooth, more or less brownish discolora- 
tion of the surface which occurs typically in fingerlike patterns 
about one-fourth of an inch in width, extending longitudinally 
toward the stylar or blossom end of the fruit. (PL I.) These 
streaks may or may not be confined to one side of the fruit, and 
frequently they appear to arise in areas russeted by rust mites 
[Eriophyes oleiveros Ashmead). The streaks are usually few in 
number, seldom more than six or eight; occasionally two or more 
merge and form a rather wide discoloration, in which event the 
injury is generally attributed to rust mites. (PI. II, fig. 1.) 

Wither-tip tear-stain as it occurs in Florida is one of the minor 
diseases of citrus fruits, and for that reason it has received little 
attention from investigators. Its effects are principally observed 
on the round orange and grapefruit, more noticeably and frequently 
on the latter and to a less extent upon other economic species of 
citrus. 

15580°— 21— Bull. 924 



2 BULLETIN 924, U. S. DEPARTMENT OF AGRICULTURE. 

The economic importance of this blemish is chiefly due to the 
financial loss which the grower sustains as a result of the lowered 
market value of the affected fruit, which is rendered unsightly and 
unattractive. However, tear-stained fruit seems to possess flavor 
and keeping qualities essentially equal to fruit which is free from 
these markings. 

REVIEW OF THE LITERATURE. 

A careful survey of the literature reveals the fact that very little 
has been published on the subject. The cause of tear-stain was 
investigated and first reported on by Rolfs (7), 1 who is quoted as 
follows : 

This peculiar form of russeting manifests itself by streaks running over the fruit. 
from the side that hangs uppermost to the point which is nearest the ground. The 
cause of this peculiar form of russeting is that somewhere above the fruit a twig 
occurs which has been infested by the fungus 2 and which contains the hold-over 
spores. Whenever sufficient rain or dew occurs to cause a dripping from the disease- 
infected twig on to the fruit, the disseminating spores are liberated from the twig 
and earned with the rain or dew over the epidermis of the fruit. Many of the spores 
are left along in different places, and these produce sufficient irritation to the epi- 
dermis to cause russeting along in streaks; hence we have the peculiar form of tear 
staining or tear streaks. 

Again in 1911 Rolfs (8) discussed the subject as follows: 

Russeting and tear streaking can nearly always be traced back for their beginning 
to a small dead spur or sprig. The fungus 2 lives in the dead spur or sprig. Water 
from rains and moisture following heavy dews collect in drops on these sprigs or 
spurs and the drops when they fall carry with them numerous fungous spores. These 
spores come in contact with the epidermis of the fruits and germinate, causing 
minute lesions on the epidermis, too small for complete infection and the production 
of anthracnose. 

This explanation as presented by Rolfs, to the effect that C6l~ 
letotrichum gloeosporioides is the responsible agent, seems to have 
been accepted by several investigatqrs at various times, among 
them Fawcett (2-5), Stevens (9), Stevenson (10), and Matz (6). 

On the other hand, Earle and Rogers (1) recognized in the Isle 
of Pines two types of russeting or tear staining said to be easily 
distinguishable, the one attributed to rust mites and the other 
thought to be caused by a fungus. In discussing wither-tip they 
make the following statement: 

One of the serious troubles attributed to the wither-tip fungus in Florida is that 
water washing down from infected twigs will cause the serious discoloration of the 
fruit known as tear streaking. The discoloration is often confused with the work of 
the rust mite, though it is easily distinguished. It frequently occurs here and can 
be always traced to some dead twig, but we are still uncertain whether it is due to the 
secretions of the wither-tip fungus or the Diplodia. 

• The serial numbers in parentheses refer to '• Literature cited " at the end of this bulletin. 
i iillitotrichum gloeospori< U'< s ii.eiilionni in the context q 

FEB 281921 

ooGUMH&wrs division 



<\J° TEAR-STAIN OF CITEUS FRUITS. 6 

The publications cited contain practically all the more important 
references to wither-tip tear-stain in Florida or near-by sections where 
the round orange and grapefruit are grown in large quantities, and no 
presentation of actual experimental data is made therein on which the 
fungus theory regarding the cause of tear-stain is based. However, 
it can not be denied that this theory, first stated by Rolfs, is eo plaus- 
ible that it has been accepted readily without the support of published 
experimental data. It was not until results very strikingly incon- 
sistent with this theory appeared in experimental spraying tests that 
its validity was questioned, and this has led to a thorough investiga- 
tion of the causation of the type of injury commonly known in Florida 
as "wither-tip tear-stain." The evidence presented in this bulletin 
indicates that Colletotrichum gloeosporioides is not responsible for 
tear staining in Florida. If this fungus ever produces such an 
effect, it must be extremely rare in that section. 

SPRAYING EXPERIMENTS. 

During the season of 1917, in connection with spraying experiments 
which were conducted in a bearing grapefruit grove for the control of 
citrus scab, it was observed that tear r.taining was almost entirely 
absent from those plats that received several applications of lime- 
sulphur solution, though it was quite prevalent where Bordeaux 
mixture had been applied during the scab-spraying season. Since 
this first observation, many similar manifestations of the lack of 
control of tear-stain by copper sprays have appeared in the experi- 
mental plats. Such a failure has been proportional to the severity 
of rust-mite attack. 

Ordinarily the scab-spraying season in Florida begins in February 
when the spring growth starts and extends over a period of two or 
three months. It is followed rather closely by the period of very 
severe attack by rust mites. The latter are usually most abundant 
during May and June and are readily controlled by two or three appli- 
cations of lime-sulphur solution diluted 1 to 66. With this explana- 
tion the data in Table I can be readily interpreted. 

In general, the results of this spraying experiment show (1) that 
tear-stain was controlled on plats 3 and 5, which received applications 
of lime-sulphur solution shortly before the period of maximum abun- 
dance of rust mites; (2) that tear-stain was materially reduced on 
plat 4, which received applications of lime-sulphur solution consid- 
erably in advance of the period of maximum numbers of rust mites; 
(3) that tear-stain was not reduced on plats 1 and 2, which received 
spray applications of copper mixtures. Assuming that tear-stain is 
caused by a species of Colletotrichum or other fungus, it would be 
reasonable to expect that plats 1 and 2 would show at least as good 
control as plat 4. The fact that control of tear-stain was so closely 



BULLETIN 924, U. S. DEPARTMENT OF AGRICULTURE. 



associated with rust-mite control is strong evidence that rust mites 
might be largely concerned in the causation of the condition that is 
generally recognized as wither-tip tear-stain. 

Table I. — Effect of various sprays on, the control of tear-stain on grapefruit. 



Date. 



1917 

Jan. 29 

Mar. 23 

Apr. 7 

May 2 and 22.. 

June 



1918. 
February (final count of 
1,000 'fruits), 1 car- 
stained, per cent . 



I'lat designation and spray application. 



No. 1, 

Bordeaux 
mixture. 



3-4-50. 
3-4-50. 
3-4-50. 
3-4-50. 



Not 
sprayed. 



No. 2, 
Burgundy 

mixture. 



3-3i-50.... 
3-3 V50.... 
3 :; ( 50... 
3-3^-50... 

Not 
sprayed. 

3S.2 



No. 3, 
Bordeaux 
mixture. 



3-4-50 

3-4-50 

3-4-50 

Lime-sulphur, 

1-40. 
Lime-sulphur, 
1-66. 

1.3 



No. 4, 
lime- 
sulphur. 



1-40 

1-10 

1-40 

Not 

sprayed. 
do... 



No. 5, 
lime- 
sulphur. 



1-40.... 

1-40 

1-40.... 
1-40.... 

1-66.... 



No. 6. 



Not spraved. 
Do. 
Do. 
Do. 

Lime-sulphur, 

1-66. 

25.9. 



a The excessive number of tear-stained fruits on the plat sprayed with Bordeaux mixture may be 
explained by the fact, quite frequently noted, that rust mites become unusually abundant on trees sprayed 
with that material. The injury did not resemble Bordeaux russet, but was similar in every respect to the 
tear staining on plat 6. 

A part of a grove of grapefruit was sprayed experimentally in June, 
1919, using 3-4-50 Bordeaux mixture for plat 1 and 1-G6 lime-sulphur 
solution for plat 2. Plat 3 was an unsprayed check. This grove had 
not been sprayed previously that season. At the end of July the 
fruit in plat 2 was free from tear staining, but numerous tear-stained 
specimens were observed in plats 1 and 3. The fiuit on these plats 
ripened and was harvested in February, 1920, with no increase of tear- 
stain over that observed in July, 1919. This indicates that one appli- 
cation of weak lime-sulphur solution applied at a time suitable for 
rust-mite control in that grove was equally effective for the control 
of tear-stain, while the standard strength of Bordeaux mixture applied 
at the same time did not reduce this blemish. (PI. II, fig. 2.) 

Other experimental data obtained during the past four years 
show without exception similar results. 

The conclusion of Yothers (11), based on numerous extensive 
experiments to control rust mites in various parts of Florida, is 
that bright fruit — i. e., fruit free from rust-mite injury — is invariably 
free from tear-stain as well. (PI. II, fig. 1.) 

Growers generally throughout the Florida citrus belt have accom- 
plished commercial control of tear-stain whenever they have con- 
trolled rust mites by following the spraying schedules established 
for these pests. 

Definite observations in commercial groves show clearly the 
following facts: (1) Where rust mites are naturally absent tear- 
stain is not observed; (2) where rust mites occur and are successfully 
controlled tear-stain is also controlled; (3) where rust mites are 



Bui. 924, U. S. Dept. of Agriculture. 



Plate I. 




Bui. 924, U. S. Dept. of Agriculture. 



Plate II. 




Fig. I.— Damage to Grapefruit by Rust Mites. 

Dark tear stains are found frequently on areas more or less rnsseted 
by rust mites, especially where' the applications of rust-mite 
sprays were delayed. For all practical purposes, both tear-stain 
and russeting are absent from fruit kept free from rust mites. 
Note the zone of faint russet. 



/ 



w 




Fig. 2.— The Work of Rust Mites on Grapefruit Sprayed in June 
with Bordeaux" Mixture. 

In the zone of rust-mite activity injury is Confined to the area not covered with spray. 
Near-by grapefruit trees sprayed on the same date with lime-sulphur solution (1-66) 
matured fruit entirely free from russeting or tear-stain. 



TEAR-STAIN OF CITRUS FRUITS. 



present and are not controlled tear-stain occurs and usually varies 
proportionately with the severity of the rust-mite attack; (4) rust- 
mite russet and wither-tip tear-stain develop simultaneously 

Usually in Florida a small proportion of late citrus blooms occur 
in June. Fruits from such blooms develop after the normal rust- 
mite period and almost invariably ripen free from tear staining 
unless rust mites happen to become abundant during the following 
winter or early-spring months. 

CULTURAL WORK. 

Fungi are admittedly capable of producing tear-streak patterns 
on the host; for example, Phomopsis citri is known definitely to 
produce melanose injury in distinct tear streaks on various citrus 
fruits. Consequently a careful study was made to determine the 
frequency of the occurrence of Colletotrichum gloeosporioides or 
other fungi in typical wither-tip tear-stain areas. 

In preliminary tests made during the fall of 1918 oranges and 
grapefruit were selected that showed typical wither-tip tear-stain, 
as well as fruit affected with rust-mite russet which shaded off into 
tear-stain. Usually 30 cultures were made from each fruit, 10 each 
from areas selected as follows: (1) Typical rust-mite russet, (2) 
typical tear-stained streaks or slightly discolored areas on fruits show- 
ing no streaking, and (3) normal areas not discolored. The fruits 
were washed 1 minute in 1-1,000 mercuric-chlorid solution and 
afterwards thoroughly rinsed in sterile water. Bits of tissue were 
then removed with flamed instruments to sterile Petri dishes and 
covered with melted corn-meal agar. These cultures were allowed 
to grow five days at room temperature. The results of this pre- 
liminary culture test are found in Table II, the percentages being 
based on the number of the bits of tissue used in each test. 

Table II. — Culture tests for the isolation of Colletotrichum gloeosporioides ' from normal 
and affected parts of orange and grapefruit rind. 



Series. 


Number 

of fruits. 


Bits of 
tissue 

cultured. 


Colletofri- 
chum 

gloeospori- 
oides. 


Miscel- 
laneous 
organ- 
isms. 


No 
growth. 




17 
16 
19 


170 
160 
190 


38.2 

21.1 

6.2 


18.8 
19.3 
15.7 


43.0 




59.6 




78.1 







1 The use of the name C ilU totrich u m glut osporioides in the culture data of this publication merely follows 
established custom and is without prejudice as to the proper designation of the organism. Any Colletot- 
richum showing characteristic growth on corn-meal agar was recorded as this species. 

It thus appears that Colletotrichum gloeosporioides is recovered 
in rather low percentage from tear-streaked areas, that it is present 
to some extent in normal as well as badly russeted areas, and that 
the frequency of occurrence varies directly with the degree of injury. 



BULLETIN 924, U. S. DEPARTMENT OF AGRICULTURE. 






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TEAR-STAIN OF CITRUS FRUITS. 7 

In the fall of 1919 a more extensive test was conducted. Fifteen 
lots of fruit were involved. Five of these lots were selected by the 
writer, and the remaining ten lots were selected in various parts of 
Florida by persons specially chosen for their competence to select 
typical rust-mite injury and typical wither-tip tear-stain. Each 
of these lots was sorted into several groups of one to four fruits 
each according to the variety of fruit, the particular type of effect, 
and the intensity of it. For a comparative study, cultures were 
made from fruits in the same lot that were free from blemishes or 
from unblemished areas on the russeted or tear-stained fruits. One 
hundred bits of tissue, approximately 1 square millimeter in surface 
area, were cultured from each test area of each fruit, using: 10 Petri 
dishes, each with 10 bits of tissue. The results when reduced to a 
percentage basis, as in Table III, also represent the average numbers 
of occurrence per fruit. Corn-meal agar was used as a culture 
medium and the plates were held six days at room temperature. 
Counts were made of the common saprophytic type of Cladosporium 
as well as of Colletotrichum colonies. Bacteria and fungi other 
than these were reckoned as miscellaneous. Two parallel series 
were made, one for undisinfected tissue and one from similar areas 
on the same fruits washed with a disinfectant. Bichlorid of mercury 
solution (1 to 1,000) was used for 1 minute with subsequent rinsing 
on all disinfected lots except K, L, and M; on these three lots undi- 
luted fresh hydrogen peroxid was used without rinsing. Table III 
gives the results, with fractions omitted for the higher percentages. 

Table III shows that Colletotrichum <jloeosporioid.es is practically 
universally distributed on citrus-fruit surfaces and that it escapes to 
a considerable degree the surface disinfection process ordinarily prac- 
ticed in culture work. It is present about equally on the average in 
tear-stained and russeted areas. The amount varies in different lots 
of fruits, but seems to be more abundant where the visible effects 
are most pronounced. A saprophytic type of Cladosporium is isolated 
with the same constancy as Colletotrichum gloeosporioides, but with 
less frequency. These extensive culture tests show, therefore, that 
it would be about as reasonable to ascribe the blemishes to one of 
these organisms as to the other, if constancy of isolation from lesions 
is to be the deciding consideration. However, neither fungus reaches 
a frequency of occurrence high enough to justify holding it to be 
the causative organism on this evidence alone. 

Certain fruits having the melanose type of tear-streak were 
selected, and cultures were made from these in the manner already 
described, comparative tests being made from unblemished areas, 
from melanose tear-streak, and from diffused melanose areas; and 
cultures from the surface blemish known as "shark skin" were also 
made. The results are given in Table IV. 



8 BULLETIN 924, U. S. DEPARTMENT OF AGRICULTURE. 

Tasle IV. — Isolation of Colletotrichum gloeosporioides, Cladosporium sp., and miscel- 
laneous organisms from orange and grapefruit rind affected with melanose or with 

■shark skin." 





\ and v. 


Remarks. 


Series A , diffused 
patches. 


Series B, tear- 
streak pattern. 


Series C, un- 
blemished. 


Lol and num- 
ber of fruits 
in group. 


eg 

j=3 

o a 
© o 

o.2 

O Ml 


i 

C 
o 
ft 
o 

5 


5 
a 

'© 

S 


S ft 

o o 


p 
"C 

o 

o 

s 


5 

1 

1 


1 2 
0.2 

43 
ft 
J2 




| 


ft 

■d 

O 



a 
— 


'I 


N ot d i s i n- 
fected: 
Lot E, 4 


Grapefruit, 
do 


Melanose tear streaks - 

Bright area on mela- 
nose fruits. 
Melanose tear streaks . 

do 









40 


11 


51 








fruits. 
Do... 


27 
12 


23 
5 


40 


Lot G, 2 

fruits. 
Lot L, 2 


do 

do 

do 

Orange 

< rrapefruit. 

do 

do . 






s 


11 

2 


45 
1 


15 


fruits. 
Lot N, 1 

fruit. 
Lot J 4 


Mud-caked melanose. 

Decided "shark skin" 

do 


32 

31 
25 


19 
17 
1.-, 


C7 
40 

n 


















fruits. 

Lot K, 4 

fruits. 

Oisinfected: 

Lot E, 4 

fruits. 

Do 












Melanose tear streaks. 

Bright area on mela- 
nose fruits. 
Melanose tear streaks . 

do 




1 
















6.5 


.5 


.3 


Lot G, 2 

fruits. 
Lot L, 2 

fruits. 
Lot N, 1 

fruit. 
Lot J, 4 

trails. 
Lot K, 4 

fruits. 


do 

do 

do 

< (range 

< rrapefruit. 








36 

5 


7 


1 


2 










Mud-caked melanose . 

Decided "sharkskin''' 

do 


f . 5 

19 


2 

1 


l 
l 
3. 5 



































It appears from Table IV that olhtotrichum gloeosporioides is 
recovered with about the same frequency as is shown in Table III, 
thus indicating that no positive conclusion as to the causation of 
tear-stain can be reasonably based on isolation tests. 

All the cultural work shows that Colletotrichum gloeosporioides 
has an isolation percentage from tear-stained areas rather too low 
for it to be the active pathogen and that this organism is present 
to some extent on normal as well as badly russeted areas, the fre- 
quency varying with the degree of injury. 

The fungi in various types of miscellaneous lesions on citrus fruits 
were examined by similar cultural methods. These lesions included 
spray-burn scars, hail bruises, thorn scratches, and old citrus-scab 
lesions. The fungous flora was very similar to that obtained from 
tear-stained and russeted areas. Colonies of Colletotrichum pre- 
dominated, the saprophytic Cladosporium ranked next, while col- 
onies of bacteria and various other fungi occurred in smaller numbers. 



TEAR-STAIN OF CITEUS FRUITS. 9 

HISTOLOGICAL EXAMINATION. 

To the unaided eye, rust-mite russet with its several patterns and 
the so-called wither-tip russet or tear-stain intergrade imperceptibly. 
Ordinarily the grower calls the streak tear-stain and the solid area 
rust-mite russet. 

It was deemed important to make careful microscopic examina- 
tions to determine whether distinctive features exist in the rind 
tissue of the affected parts. Fruits were examined showing typical 
patterns of rust-mite russet as well as those showing several degrees 
of the so-called wither-tip tear-stain. Under the microscope there 
appears to be no material difference between these types of injury. 
The examination of the injured parts in both instances indicates 
that the cuticle and epidermal cells appear to be punctured, and 
beneath, depending upon the degree of russeting, one to three layers 
of cells, together with their contents, are of a rusty brown color. 
Quite frequently mycelial threads and spores of fungi are found 
adhering to the affected parts. These fungi prove to be the types 
commonly found on citrus, such as species of Colletotrichum and 
Cladosporium. 

The histological examinations have not revealed any feature that 
would serve to distinguish between the rust-mite russet and the 
so-called wither-tip tear-stain. 

The presence of punctures in the epidermal cells of the tear-stained 
areas would strongly suggest the work of sucking parasites rather 
than that of parasitic fungi. This suggestion is further substantiated 
by the following observation: In July, 1919, by the aid of a hand 
lens, numerous tear-stained immature grapefruits wore examined 
while still hanging on the tree in an unsprayed grove near Orlando, 
Fla. The rust mites and their castings were more or less generally 
distributed over the fruits, but were present in especially large 
numbers over the tear-stained areas. This condition was very notice- 
able early in July. By August 2 such a marked segregation of 
mites in streaks was not particularly evident, and the mites them- 
selves, as well as their castings, were nowhere present in very large 
numbers, but the tear stains, presumably caused by rust mites 
were quite evident. 

INOCULATION EXPERIMENTS. 

An inoculation experiment was conducted the last week in June, 
1919, on immature grapefruits which were about 2 inches in diameter 
and so far as could be determined free from blemishes. Fifty fruits 
were used in this experiment. The inoculum was derived in part 
from dead sweet-orange twigs which had been held in moist chambers 
and on which developed a copious growth of the wither-tip fungus 
and in part from pure cultures of Colletotrichum gloeos porioides , 



10 BULLETIN 924, U, S. DEPARTMENT OF AGRICULTURE. 

which had been isolated from an injured grapefruit leaf. The 
spores were washed off the twigs and mixed with those from the 
culture tubes. This wash water, which was clouded with fresh viable 
spores, was used in saturating wads of absorbent cotton, which, in 
turn were placed on the fruit. The inoculated fruit was covered 
with two or three layers of waxed paper for 4S hours. At the 
expiration of this time the paper and wet cotton were removed and 
the fruit left unprotected. To serve the purpose of a control, other 
fruits were similarly treated, except that the cotton was wetted 
with sterile water. These inoculations gave negative results. 

Similar inoculation tests were made during the fall of 1919, using 
as inoculum a mixture of a number of strains of CbUetotrichum gl 

solated from typical tear stains on grapefruit and from 
dead grapefruit twigs, as follows: 

On October 20. 1919. on almost fully grown grapefruit: on October 27. on grapefruit 
showing faint yellowing: on November 7, on grapefruit approximately one-half colored; 
on November 15. on grapefruit almost fully colored: and on December 3. on mature 
grapefruit. This test was repeated during the late spring, summer, and fall of 1920, 
using mixed inoculum from the same strains of CoUetotruhum gloeosporioides. Inocu- 
lations were made on May 15, on grapefruit averaging 1 inch in diameter: on May 21, 
apefruit a - ; inches in diameter: on June 15,' on grapefruit averaging 

- in diameter: on June 30. on grapefruit avers . . . _ inches in diameter: 
on July 15. on grapefruit averaging 2^ inches in diameter: on July 30. on grapefruit 
averaging 3 inches in diameter: and on November 1 and 6. on grapefruit just be- 
ginning to color. 

The results of all these tests were negative. Not the slightest 
symptom of tear-stain in any of the fruits inoculated during 1919 
could be detected as late as February. 1920. when the crop was har- 
vested. The fruit inoculated during 1920 was free from tear-stain 
when final observations were made in November. 

Observations were made to determine the frequency of association 
of tear-stain with dead twigs that might harbor Collet otrichum or 
other fungi. Unsprayed groves with more than the average propor- 
tion of dead wood present were examined carefully during the past 
four years. Among the properties inspected in Florida 4 are in Lee 
County. 10 in Polk County. 2 in Hillsboro County. 3 in Pinellas 
County. 3 in Osceola County. 10 in Orange County. 2 in Volusia 
County, 4 in Brevard County, 3 in St. Lucie County, and 4 in Dade 
County. The data obtained indicate that dead twigs, spurs, etc.. are 
found immediately over not more than 10 per cent of the tear-stained 
fruit, and that in damp, densely shaded, low-hammock properties, 
where trees have an unusually large number of dead twigs and where 
environmental factors would appear to be especially favorable for the 
development of fungi, tear-stained fruits are very seldom found. On 
the other hand, tear-stain is most abundant in higher and drier lo- 
cations where lijht and moisture favor the greatest rust-mite 
development. 



TEAR-STAIN OF CITKUS FRUITS. 11 

CONCLUSIONS. 

While the foregoing evidence i- to the effect that tear staining of 
Florida citrus fruits is caused by rust mites rather than by the fungus 
CoUetotrichum gloeosporioides, as claimed by Rolfs, it must be admitted 
that the writer may not have seen all types of this injury. However, 
if a special type of tear staining caused by this fungus occurs in Florida 
it must have been exceedingly rare during the past four years to have 
escaped detection by the writer. The experimental and observational 
data on the control of what has been regarded as wither-tip tear-stain 
by investigators and Florida growers seems to be definite enough to 
warrant the conclusion that practically all of the so-called wither-tip 
tear-stain in Florida is caused by rust mites and can be readily con- 
trolled by controlling these pests. 

SUMMARY. 

1 Pure cultures from typically tear-stained fruit show that ( 61- 
,,, gloeosporoides is not confined characteristically to the tear 
streaks, but is even more prevalent on the larger russeted areas and is 
almost invariably found on normally colored areas. 

(2) Inoculations on grapefruit in various stages of development 
with cultures of the fungus CoUetotrichum gloeosporioides failed to pro- 
duce tear streaks or other positive reaction. 

(3) Dead wood that might harbor < bUetotrichum gloeosporioides was 
found associated with not more than 10 per cent of the affected fruit. 

(4) It is impossible to distinguish by histological methods between 
the ordinary rust-mite russet and so-called wither-tip tear-stain. 

(5) Rust mites were found very abundant in recently developed 
tear-streak patterns on grapefruit. 

(6 ) Spring-bloom fruit on unsprayed trees usually becomes seriously 
tear stained: June-bloom fruit on such trees usually ripens free from 
these markings. 

(7) Copper sprays applied in the spring and not followed by rust- 
mite applications of sulphur sprays tend to increase tear staining, 
but when followed by rust-mite applications no appreciable amount 
of tear staining develops. 

(8) When sulphur sprays are applied during the early spring, 
which is usually too early for the best rust-mite control, and are not 
followed by the regular rust-mite application tear staining is greatly 
reduced. 

(9) When only the rust-mite applications are made, tear staining 
is practically eliminated. 

(10) The same local and seasonal conditions of moisture and light 
that favor rust-mite injury also favor tear-stain. 

(11) Practically all of the so-called wither-tip tear-stain in Florida 
is associated with rust mites and can be readily controlled by con- 
trolling these mites. 



L2 



BULLETIN 924, U 



HEPAFTMK^T OF AGRICULTURE. 



LITERATURE CITED. 

1 F.aki.e, F. S., and Roger-. J. M. 

1915. Citrus pests and diseases at San Pedro in 1915. In San Pedro Citrus 
Path. Lab., 1st Ann. Rpt.. 1915, p. 5-41, 19 fig. 
Fawcett. IPS. 

1910. Summer pruning for wither-tip. Fla. Agr. Exp. Sta. Press Bui. 151, 

2 p. 
1912. Report of plant pathologist. In Fla. Agr. Exp. Sta. Rpt. [1910] 11, 
p. Iviii-lxvii. 

1914. Citrus diseases. In Sth Ann. Rpt., Cuban Nat. Hon. Soc, 1911. 

p. 21-30. 

1915. Citrus diseases of Florida and Cuba compared with those of California. 

Calif. Agr. Exp. Sta. Bui. 262, p. 149-210. 24 fig. 

Matz, Julius. 

1919. Citrus spots and blemishes. Porto Pico Dept. Agr. and Labor, Insular 
Exp. Sta. Circ. 16, 8 p., 3 col. pi. 
Rolfs, P. II. 

1905. Report of committee on diseases of Citrus. In Proc. 18th Ann. Meet- 
ing Fla. State Hort. Soc., 1905, p. 29-32. 

1911. Russeting and tear streaking caused by wither-tip fungus. In Fla. 

Agr. Exp. Sta. Bui. 108, p. 30-32, fig. 12-13. 

- EVENS. II. E. 

1918. Florida citrus diseases. Fla Agr. Exp. Sta. Bui. 150, p. 13-110, 
fig. 7-54. 

■ KX SON. J. A. 

1918. Citrus diseases of Porto Rico. In Jour. Dept. Agr., Porto Rico, v. 2, 
no. 2. p. 43-123, 23 fig. 

I 11 YOTHERS, \V. W. 

1918. Spraying for the control of insects and miu>s attacking < itrus trees in 
Florida. L T . S. Dept. Agr., Farmers' Bui. 933, 3.8 p., 24 fig. 



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